Japanese maple

Acer palmatum is the tree most people picture when they think of bonsai, and for good reason. Few species reward patient ramification work so visibly. A well-developed Japanese maple has a delicate twig structure that's clearly visible in winter, soft fresh green in spring, dense canopy in summer, and fiery autumn colour that holds for two or three weeks if the weather behaves.

It is, however, not quite a beginner tree. Maples in pots are more vulnerable than maples in the ground — to dry roots, to wet roots, to afternoon sun, to late frosts on opening buds, to wind. None of these is hard to manage once you understand them, but a forgotten watering on a hot July afternoon can scorch leaves badly, and a frozen pot in February can kill a tree outright. Treat it as a tree that wants attention rather than one that tolerates neglect.

Maples need consistently moist, well-drained soil through the growing season. In practice this means checking every morning from late April through October. Water thoroughly when the surface of the soil starts to feel dry — water until it runs freely from the drainage holes, then water again a minute later.

In July and August you may need to water twice a day, especially for trees in shallow pots or trees in full leaf after a defoliation. A pot that goes bone-dry for half a day in summer will scorch the leaf margins, and once scorched they don't recover that season.

Equally, don't keep the soil wet in winter. From November to February the tree is dormant and a saturated pot in cold weather invites root rot. Tilt pots slightly so meltwater drains; if you've had heavy rain followed by a freeze, check that drainage holes aren't blocked with ice.

Use rainwater where possible. Hard tap water (most of southern England) gradually shifts the soil alkaline over years, which maples dislike. If you only have tap, that's fine — just repot on a slightly shorter cycle.

Maples are moderate feeders. Begin liquid feeding once leaves have fully opened and hardened off — typically mid-to-late April in southern England, early May further north. Use a balanced liquid feed at half the recommended strength, weekly through to mid-August. After that, switch to a low-nitrogen autumn feed (high P and K) for three or four weeks to help the wood ripen for winter, then stop.

Slow-release organic pellets (biogold, green king or similar) work well as a supplement — apply in spring and again in early summer, but stop in late July. Continued high-nitrogen feeding into autumn pushes soft late growth that won't harden before frost and produces coarser internodes.

On young, developing material you can push harder. On refined trees where you're maintaining ramification rather than building it, feed lightly — overfeeding is the fastest way to get long internodes and oversized leaves on a finished tree.

Japanese maples want a free-draining, slightly acidic, moisture-retentive substrate. The Japanese standard is akadama-dominant, and there's no good reason to argue with that for this species.

Repot every 2–3 years for young, vigorous trees; every 3–5 years for mature, refined specimens. The single most important factor is timing: repot just as the buds swell and show colour but before they break into leaf. In southern England this window is typically late February to mid-March. In Scotland and the north, mid-to-late March. Miss the window and you'll either disturb dormant roots in cold soil (slow recovery) or work on a tree that's already pushing energy into new leaves (severe setback).

When repotting, work the root ball out, comb the roots radially with a root rake, and cut back no more than a third of the root mass on healthy trees. Older trees tolerate less root work — be conservative. Wash the cut surfaces with water, settle the tree into fresh substrate, and water in heavily. Keep the freshly repotted tree out of wind and direct sun for two or three weeks.

Do not repot in autumn. The advice you sometimes see online about autumn repotting comes from warmer climates and doesn't apply here — UK winters are too wet and the tree can't establish new roots before dormancy.

Structural pruning happens in winter while the tree is dormant and you can see the silhouette clearly — December or January is ideal. Major cuts heal faster if made just before spring sap rise. Use a concave cutter for branches over pencil-thickness, and seal larger wounds; maples can die back from poorly sealed cuts.

Through the growing season, the main job is shoot pinching. Once a new shoot has hardened to four or five leaves, pinch it back to two. This is what builds the fine ramification maples are famous for. Don't pinch every shoot — leave some to extend if the tree needs vigour, especially in weaker areas of the canopy.

Defoliation (removing all leaves in early summer to force a second flush with smaller leaves) is a refining technique, not a developing one. Only defoliate healthy, well-fed trees and only every 2–3 years. Late June is the window in the UK. Don't defoliate a tree you've just repotted, or one showing any sign of stress.

Wire after leaves have hardened in early summer (June) or in winter on bare branches (December–January). Bark marks easily — maples scar faster than almost any other bonsai species — so use anodised aluminium wire, apply it loosely, and check weekly through the growing season. Remove wire as soon as it begins to bite, not when it's already cut in.

Smooth-bark cultivars (deshojo, kiyohime) mark even faster. On these, raffia-wrap the branch before wiring anything substantial.

Maples lend themselves to most informal styles — informal upright (moyogi) is the classic, but broom (hokidachi) suits cultivars with a naturally upright habit like Acer palmatum 'Kiyohime'. Twin-trunk, clump, and forest plantings (yose-ue) are all traditional. Cascade and semi-cascade are rare for maples and don't really suit their natural growth habit.

Aim for a soft, flowing line in the trunk and a canopy that breaks slightly under its own weight — that "old tree in a meadow" feel rather than anything sharp.

Roots in a pot are vulnerable in ways that roots in the ground are not. A Japanese maple in the ground in the UK is fully hardy; the same tree in a pot can be killed by a hard frost.

From November onwards, move trees out of wind. Below -5°C, get them into an unheated greenhouse, cold frame, or sheltered porch. The goal is to protect the roots and the swelling buds from desiccating wind and prolonged hard freezes — not to keep them warm. Bringing a maple indoors over winter will kill it within a season or two; it needs the cold to set buds properly.

A simpler alternative: bury the pot in a sheltered raised bed, mulched with bark or leaf mould. The tree's foliage is gone by then so the pot can sit anywhere shaded.

From cuttings (semi-hardwood, June, with rooting hormone — variable success), from seed (autumn-sown, cold-stratified — true to species but not to cultivar), or by air layering (May–June on hardwood, ringed bark, sphagnum, plastic, take a year). Air layering is the most reliable way to get a substantial nursery-stock tree into a quality bonsai trunk quickly.

Maples are reasonably trouble-free if watered correctly and not stressed. Most problems trace back to too much sun, irregular watering, or saturated winter roots.